Treatment of acid sludge



Aug'. 31, J. M. RUMPLE l l 2,091,937

TREATMENT 'OF ACID sLUDGE Filed De. 6 1933 l com?" BY l /T MW ATTORNEY.

Patented Aug. 31, 1937 UNITE S'i'ii OFIQE TREATMENT F ACID SLUDGEApplication December 6, 1933, Serial No. 791,137

` 11 Claims.v

scribed in the copending application Serial No.l

568,050, Was led October 10, 1931, now Patent No. 1,953,225, dated April3, 1934. This process heated acid sludge with combustion gases in arotary kiln and very satisfactory results `Were produced with acidsludges of high acid content. It was possible to obtain a gas containingvery satisfactory proportions of SO2 for use in the con- .,0 tactsulphuric acid process, but considerable difficulties were encounteredwith the removal of hydrocarbons from the gas and the process did notprove as well suited for high oil or low acid sludges as for the highacid sludges. Various 5 modiiications of the i-Ieclienbleikner processhave been developed to avoid difculties encountered by the presence ofhydrocarbons in the gas. Thus, for example, in the copending applicationof Hechenbleikner and Mast, Serial No. 693,136, iiled October 11, 1933,the uncondensable hydrocarbons are burned out in the hydrocarboncombustion furnace. This method, which is entirely satisfactory withhigh acid sludges, however, cannot be employed with sludges Whiehcontainexcessive quantities of oil as the amount of hydrocarbons which wouldhave to be burned is too great and the dilution With carbon dioxide andnitrogen by the combustion process renders the iinal gas too dilute forsatisfactory operation in the co-ntact sulphuric acid process. Even withhigh acid sludges the Hechenbleikner process requires considerableequipment for purification of the gas and is suitable primarily Where agas of moderate or low SO2 content is desired for it is, of course,impossible with the straight Hechenbleikner process to produce from thekiln a gas having very high concentrations of SO2 since the gas isnecessarily diluted with the relatively quite large Volumes ofcombustion gases employed in heating the sludge.

While the production of a strong SO2 gas from acid sludge is oiparticular importance When the gas is to be utilized in the contactsulfuric acid process, this is not the only ,process in which a strongSO2 gas desirable. Thus, forexample,l

when an SO2 gas contains hydrocarbons it should be treated to remove thehydrocarbons before using in the chamber process for sulfuric acidbecause of the loss of nitric oxides which other- Wise results. Manyother uses for SO2 such as, for example, the production of liquid SO2 bycondensation requiring relatively strong gas for good eiiiciency and thestrong SO2 gas produced by the present invention opens up such fields toSO2 gases from acid sludge. Even in processes Where a strong gas is notessential such as, for example, in the production of bisulfites, thestronger the gas the greater the capacity of given apparatus. Thepresent invention is therefore not limited to processes Which cannot becarried out with a dilute impure SO2 but also includes processes which.can utilize a dilute SO2 but in which the stronger gas of the presentinvention makes for better economy,

The present process produces an SO2 gas of great strength in some casesup to 80 or 90% of SO2 and can be used with equal efficiency on high oilor loW oil sludges or in fact on sludges of any type. Essentially thepresent invention differs` from the Hechenbleikner process in thatinstead of using combustion gases as a source of heat to decompose thesludgev in the kiln, the stream of gaseous products from the kiln istreated to separate Water and condensable hydrocarbons and then isrecirculated through the kiln, after being heated up in suitable stovesor heat exchangers. In this manner since the SO2 gas is used as theheating agent a high percentage of SO2 rapidly builds up and a portion,of course, is continuously removed from the circuit. This processpermits operating with sludges of almost any type since even when theamount of hydrocarbons is very high, by far the major portion of thehydrocarbons volatilized can be condensed which is impossible with theordinary Hechen bleikner process. owing to the heavy dilution withcombustion gases which results in the formation of hydrocarbon mistwhich cannot be adequately removed in condensers of reasonable size.y'I'he present process having no large Volume of dilution gases andcorrespondingly a relatively very slow circulation speed, can be freedfrom practically all condensable hydrocarbons in a very smple manner sothat it is practically immaterial to the satisfactory operation of theprocess whether the sludge used contains small or large amounts ovolatilizable hydrocarbon material, Whereas in the straightHechenbleikner process the presence of large `amounts of hydrocarbons 55very seriously interferes with the operation and requires elaborateequipment for handling it.

While the present invention is in no sense limited to the treatment ofhigh oil sludges, it 5 being advantageous even with high acid sludgeswhich can be satisfactorily treated by the Hechenbleikner process, inits preferred embodiment it is particularly adaptable for use with suchhigh oil sludges which are difficult to handle by other processes.

The production of a Very strong SO2 gas opens I up further advantagesfor the present process. Thus, for example, if the SO2 is to be reducedto sulphur, as described and claimed in the copending application of C.B. Clark, Serial No. 675,973, led June 15, 1933, the present process isparticularly useful because the success of sulphur processes depends toa considerable extent on the concentration of SO2 gases availablebecause the cost oi iinal recovery of sulphur becomes prohibitive wherethe gases are too dilute. While the strong SO2 gas can be purified andthe small amount of residual hydrocarbons removed by the same methods asare used in the Hechenbleikner process or in some cases the amounts ofhydrocarbons are small enough so that they do not cause difliculty inwater formation in the contact sulphuric acid process, as described andclaimed in the co-pending application of C. B. Clark, filed May 9, 1933,Serial No.

670,123, now Patent No. 2,019,893, dated November 5, 1935, the stronggases of the present invention lend themselves to a dierent method ofpurication which produces highly purified SO2 gases. This methodconsists in absorbing t the crude SO2 in water and driving out pure SO2I therefrom by means of hot air so that a gas is produced suitable forthe contact sulphuric acid process. It should be understood that I donot claim as my invention this method of stripping per se which formsthe subject of the copending application of W. L. Spalding, Serial No.709,558, led February 3, 1934. In the present application this method ofpurifying SO2 is claimed only in conjunction With the sludgedecomposition system forming the main features of the present invention,but in a more specific aspect this method of purication is covered inconjunction with the present process since it provides adequatepurication with very simple equipment and results in a gas of mostfavorable composition for the contact sulphuric acid process or forother uses requiring strong SO2 gases.

The strong gas of the present invention may be used in a contactsulphuric acid process entirely apart from other sources of SO2 or itmay be combined with SO2 from a Hechenbleikner process Where thecombination will result in a suiiicient dilution of the hydrocarbonsremaining in the gas from the Hechenbleikner process to render theirremoval by the Hechenbleikner and Mast process unnecessary. Thiscombination is not claimed in the present invention broadly but formsthe subject matter of the copending application of C. B. Clark, SerialNo. 671,647, filed May 18, 1933, now Patent No. 2,044,419, dated June16, 1936. Such a combined process is of importance where a relativelylarge volume of high oil sludges are encountered together with some highacid sludges and particularly where a Hechenbleikner plant is already inoperation and it is desired to add toit units capable of handlingsludges which are higher in oil.

The present process possesses the advantages of the I-Iechenbleiknerprocess with regard to the production of a useful fuel from the sludge.This coke may be sold or it may be used as part of the fuel for heatingthe circulating gases of the present process. It is an advantage of thepresent process that the design of heater or stove for the circulatinggases. can be of any suitable type and can readily be adapted to heatingby solid fuel, whereas for compact units ci the Hechenbleiknen process,in which combustion gases from a furnace are sent through the kiln, itis normally preferable to use a liquid fuel. The complete independenceof the present process in the matter of fuel characteristics is animportant advantage where the oil renery may be so situated as to haveno market for the coke produced.

The present invention is not dependent on any particular mechanicaldesign of apparatus. The drawing, which is for the most partdiagrammatic in form, merely shows typical arrangements, but the processcan be used in other mechanical arrangements and it is an advantage ofthe present invention that it is very exible and adaptable to the mostvaried types of installations and operating conditions.

In the drawing Figure 1 is a diagrammatic elevation of a plant usingstoves as a heating means; and

Figure 2 is a diagrammatic elevation with the heat exchanger in sectionof a plant utilizing a continuous heat exchanger for heating the gasstream.

In the design shown in Fig. 1 the sludge is caused to flow from thesludge inlet 2 through the kiln I where it encounters a countercurrentflow of heating gases from the pipe 3. 'Il'ie sludge is decomposed inzones as described in the Hechenbleikner patent above referred to and acoke is discharged at the opposite end of the kiln through the cokedischarge 4. In order that the operation of the kiln may be betterunderstood the following description thereof, taken from theHechenbleikner patent, is presented:

The gases may be introduced into the retort at a temperature of about1600 F., and the flow of the feed sludge as Well as the sludge body maybe so controlled (along with the control of the gas flow) as to createthree zones of reaction, one for the evaporation of water and any lightdistillates, another for electing the main reaction of the sludge toreduce the sulphuric acid and sulphate compounds therein to SO2, and athird zone for the nal disintegration oi the sludge residue and theremoval therefrom of any occluded and/or residual gases. temperaturerange may be, for example when treating a blended liquid sludge, from212 to 300 F.; in Zone II this temperature range may be, for example,from 409 to 420 F.; these temperatures being those to which the sludgeand sludge residue are heated by the hot gases.

The main reaction of the organic matter of the sludge, the combustiongases and the sulphuric acid content of or compounds in the sludge takesplace in and around the second reaction zone, although the evolution ofSO2 begins at the lower temperatures, the evolution taking place,however, with increasing power until the critical temperature range suchas` of the order of 380 to 420 F. in the aforementioned example isreached. The direct heating of the sludge body while the latter is in anagitated and broken up state accomplishes a uniform heat treatment andavoids local overheating with its consequent In zone I the `25 stoves 9and ID.

disadvantages in producing side reactions. I

have found that with the reacting conditions in the retort, all of thereactable sulphur and HzSO4 content and compounds in the sludge are 5converted and reduced to SO2 gas., there being loing to the abovedescribed operation and containing SO2, water vapor, hydrocarbons andminor proportions of other gases, pass into a bubble tower or condenser5 where water is condensed together with condensable hydrocarbons.

- The hydrocarbons may be separated from the Water and drawn off in thecustomaryrnanner (not shown) and if desired the bubble tower may beinduplicate with the gases passing through in series as shown in theHechenbleikner and Mast application above referred to.

The puried gas containing SO2, small amounts of water vapor and verysmall amounts of hydrocarbons is driven by the blower o through thepipes 'I and 8 into one or other of the heating The flow into the stovesis through the short pipes with the valves I! and I2, respectively. Fromthe stoves the heated gas passes through the short pipes provided withvalves I3 and I9 into pipe 3 and rec-irculates through the kiln. Aportion of the gas stream is drawn off through the pipe i5 provided withthe valve IIS and the proportion drawn off is determined by the settingof the valve it and the valve I'I in the pipe 8. While the gases arepassM ing through one stove, for example 9, the valves I2 and I9 areclosed and hot gases from a coke burner I8 are passed into stove illthrough a pipe controlled by the valve 2@ and out, to a stack throughthe pipe 2 I controlledby the valve The 40 coke burner is connected tothe stove ii through the pipe 23 controlled by the valve M, which is, ofcourse, shut at this time, exit to the stack being through the pipe 25controlled by the valve 26 which is likewise closed. As the amount of,45 heat from burning the coke is. normally in excess of that requiredfor the reaction, a portion. may be by-passed tothe boiler 21 throughthe valved pipe 23 and the heat utilized in the form of steam. Whenstove 9 has cooled down and stove lil 50 has heated up, valves II, i3,3Q and 22 are closed and valves I2, i9, 2li and 25 are opened, the gasthen owing through the hot stove te while the combustion gases from thecoke burner flow through the stove 9.

The design of the stoves may be of any suitable type, but normally metalcylinders packed with re brick checker work is preferred as this type ofconstruction is Very simple and can be easily repaired. When theoperation is changed from one stove to another there is a certain amountof combustion gas remaining in the stove which is carried through thekiln. This normally does no harm, but if desired the stove can be blownout with SO2 gases by providing a suitable vent in the pipe 3.

The gas from the pipe i5 passes .in series through the absorbing towers29 and 3S) where it flows in countercurrent to a stream of water pumpedfrom the water tank yfil through the pipe 32 by means of the make up Thespent gas which contains only an infinitesimal trace of SO2 passes outthrough the vent 3ft. The cold water absorbs the SO2, forming a solutionwhich leaves the tower 29 through the pipe 35 being collected in the SO2liquor tank 3G. From this tank it is pumped through the pipe 3l by meansof the pump 3S into two packed stripping towers 39 and 4t down which itflows in countercurrent to hot air which enters through the pipe il andleaves through the pipe 472.

When the SO2 gas is to be used in the contact sulfuric acid process thishot air, which may be pre-heated from any suitable source is preferablyadjusted in temperature so that it removes an .amount of SO2, resultingin a gas mixture containing from '7 to 9% of SO2 and being suitable forthe contact sulphur acid process, except for the fact that it containsconsiderable moisture. This gas is, therefore, normally passed through adrying tower i3 before flowing to the contact plant, not shown.

The stripped liquor which contains normally not over one-tenth of apercent of SO2 may be returned to the water tank 3l. It is thenrecirculated thru the absorbing towers with the addition of sufficientwater to make up for the evaporation in the stripping towers and in theabsorbing towers. The pumping of a dilute solution of SO2 results in aslight loss of SO2 through the vent 34 and where water is cheap,slightly better overall SO2 economy is obtained by discarding the weaksolution from the stripping towers and using fresh water only.

In 'the installation shown in Fig. 2 the same parts bear the. samenumerals. This gure shows a continuous heat exchanger it taking theplace of the stoves Ei and il), the heat exchanger being of the tubulartype with tubes #liand bales lie. lThe gases from the pipe 8 flowthrough the tubes i5 over which flow the combustion gases from the cokeburner through the valved pipe 41, a satisfactory contact with the tubesbeing provided by the baflies fit which force the combustion gases tofollow a sinuous path.

This figure also shows a modication of circulation in. the stripper andabsorber towers. Instead of recirculating dilute solution from the Watertank 3l pure water is introduced into the absorbing tower through thevalved pipe iii and the dilute SO2 solution from the tank 3! is pumped.through the pipe #it by means of the pump 5i! into the bubble tower 5where the hot kiln gases remove the SO2 contained therein. As the amountof dilute SO2 solution flowing from the tank 3i is normally greater thanthat evaporated in cooling down the gases in the bubble tower 5, someliquid may be continuously drawn off from the hottest part of the bubbletower. Because of the high temperature of the bottom of the bubbletower, where .it contacts with the hot gases from the kiln, the water atthis point is practically free from any dissolved SO2.

The continuous heat exchanger shown in Fig. 2 presents numerousadvantages from an operating standpoint. In the rst place the heating iscontinuous and the temperature of the gases is therefore constant,whereas in the stoves the temperature is hotter at first and decreasesas the stoves give up their heat. The eciency of heat transfer is alsosomewhat higher because the stoves have to be heated up to a hightemperature and in the later portions of the heating cycle the heattransfer from the hot gases to the hot lire brick is, of course, poor,whereas in the heat exchanger in Fig. 2 a continuous efcient heatexchange is maintained. These marked operating advantages which reducethe amount of fuel required and make for a considerably more regular anduniform temperature in the kiln are, however, obtained at the expense ofsimplicity of construction for the heat exchanger presents aconsiderable engineering problem because of the somewhat corrosivenature of the gases circulating through it. Also it is difficult toclean and requires rather careful operation to prevent plugging withsulphur or carbon because there is a tendency for the small amount ofhydrocarbons present in the gas to react with the SO2 in the heatexchanger forming sulphur. Likewise some carbon may be produced. Withthe uniform moderate temperature in the heat exchanger, thecarbonization and sulphur formation is kept at a minimum and whenproperly operated does not cause serious trouble, but rather carefulsupervision is necessary. With the stoves a much less even heating isobtained and the tendency to form sulphur and carbon is much greaterbecause, of course, the lower portions of the stove are heated to a muchhigher temperature than the upper portions, but the stoves do notreadily plug up and can be Very easily cleaned. Both methods, therefore,present advantages and the best heating method to be used is, of course,a compromise, determined by the conditions of a particular installationand the most satisfactory method will, of course, be adopted by theskilled chemical engineer.

The absorption and stripping method shown in Fig. 2 is more eiiicientthan that shown in Fig. 1 because there is practically no loss of SO2through the vent Sil. On the other hand there is a conv siderableconsumption of water and this process,

although more ecient from the standpoint of recovery of SO2 orprevention of nuisance due to discharge of SO2 into the atmosphere, mayprove less economical where water is expensive. In such cases it ischeaper to throw away some SO2 and to use the method of Fig. l which, ofcourse, gives the maximum economy in the use of water. Both systemsoperate effectively and the choice will be determined by economic andoperating factors. Both systems have been illustrated, one in onei'igure and one in the other, but it should be understood that there isno particular connection between the specific method oi heating thecirculating gases and the specific method of absorbing and strippingshown. Thus, for example, in .one plant it may be more desirable to usethe stripping and absorbing method of Fig. l with the continuous heatexchanger of Fig. 2 and vice versa.

While the invention has been illustrated specically in the drawing in aform in which the circulating gases are practically free from oxygen(except, of course, when starting up when for the first circulation airmay be used) it should be understood that the invention is not limitedto complete recirculation. In some cases it may be desirable tointroduce a small amount of air. This is particularly true where theamount of hydrocarbons present in the circulating gas is so small thatthey can safely be burned. In such cases the introduction or" a smallamount of air into the gases in pipe il will result in burning out thehydrocarbons, complete prevention of sulphur formation and considerablesaving in fuel. The dilution resulting will not be excessive and willstill be so low as to result in the production of a sulphur dioxide gashigh enough for economical simple arrangement illustrated in thedrawing. l

It is understood, however, that the invention is not limited thereto andincludes processes in which the circulating gases are slightly dilutedwith combustion air.

What I claim is:

l. A method of producing a concentrated SO2 gas from the acid sludgefrom the sulphuric acid purication of hydrocarbonaceous material whichcomprises maintaining an undiluted recirculating stream of SO2 gas whichpasses successively through a heating stage, a sludge decompositionstage and a cooling stage, subjecting the sludge in the decompositionstage to direct contact with the hot SO2 gas from the heating stageunder conditions such that S04 components of the sludge are reduced toSO2 and volatile hydrocarbons and water are distilled off, condensingthe major portion of the Water vapor and condensable hydrocarbons fromthe gas in the cooling stage, withdrawing a portion of the resultingconcentrated SO2 gas from Ithe system and reheating the remainder in theheating stage by heat exchange with hot solids while out of contact withsubstantial amounts of diluting gases.

A method of producing a concentrated SO2 j gas from the acid sludge fromthe sulphuric acid purication of petroleum products which comprisesmaintaining an undiluted recirculating stream of SO2 gas which passessuccessively through a heating stage, a sludge decomposition stage and acooling stage, subjecting the sludge in the decomposition stage todirect contact with the hot SO2 gas from the heating stage underconditions such that S04 components of the sludge are reduced to SO2 andvolatile hydrocarbons and water are distilled oi, condensing the majorportion of the water vapor and condensable hydrocarbons from the gas inthe cooling stage, withdrawing a portion of the resulting concentratedSO2 gas from the system and reheating the remainder in the heating stageby heat exchange with hot solids while out oi contact with substantialamounts of diluting gases.

3. A method of producing a concentrated SO2 gas from the acid sludgefrom the sulphuric acid puriiication of hydrocarbonaceous material whichcomprises maintaining an undiluted recirculating stream of SO2 gas whichpasses successively through a heating stage, a sludge decompositionstage and a cooling stage, subjecting the sludge in the decompositionstage to direct contact with the hot SO2 gas from the heating stageunder conditions such that SOi components of the sludge are reduced toSO2 and volatile hydrocarbons and water are distilled on?, condensingthe major portion of the water vapor and condensable hydrocarbons fromthe gas in the cooling stage, withdrawing a portion of the resultingconcentrated SO2 gas from the system and reheating the remainder in theheating stage by passing it in contact with hot refractory materialwhile out of contact with substantial amounts of diluting gases.

5 of SO2, the solution is removed from the zone of absorption, andapuried SO2 gas is driven therefrom.

5. A method according to claim 1 in which the SO2 gas Withdrawn from thesystem is passed in Contact with an extended surface of cold Water toproduce an aqueous solution of SO2, this solution is removed from thezone of absorption, and hot air is blown through it under temperatureconditions such that a 7-9% SO2-air mixture is l5 obtained.

6. A method of producing a concentrated SO2 gas from the acid sludgefrom the sulphuric acid purification of hydrocarbonaceous material whichcomprises maintaining an undiluted recirculating stream of SO2 gas whichpasses successively through a heating stage, a sludge decompositionstage and a cooling stage, subjecting the sludge in the decompositionstage to direct contact with the hot SO2 gas from the heating stageunder conditions such that S04 components of the sludge are reduced toSO2 and volatile hydrocarbons and Water are distilled off, condensingthe major portion of the Water vapor and condensable hydrocarbons fromthe gas in the cooling stage q and reheating a portion of the resultingconcentrated SO2 gas in the heating stage by heat exchange with hotsolids While out of contact With substantial amounts of diluting gases,Withdrawing another portion of the concentrated SO2 gas from the circuitand absorbing SO2 therefrom in a solvent liquid, removing the resultingSO2 solution from the zone of absorption and expelling a purified SO2gas therefrom, and returning the solvent liquid to the absorption Zone.

'7. A method according to claim 1 in which the temperature to which theSO2 gas stream is heated is such that the sludge is not heated totemperatures at which H2S is formed.

8. A method according to claim 2 in which the temperature to which theSO2 gas stream is heated is such that the sludge is not heated totemperatures at which l-IzS is formed.

9. A method according to claim 2 in Which the SO2 gases are caused toflow over the sludge While the latter is continuously movedcountercurrent to the gases.

10. A method according to claim 2 in Which the sludge is heatedgradually in zones of increasing temperature, the first Zone being at atemperature at which Water and volatile hydrocarbons are distilled, thesecond zone at a temperature at which S04 compounds are rapidly reducedto SO2 and a third zone at a 'temperature at Which the residue isconditioned to form a useful fuel.

11. A method according to claim 1 in which the gas stream is heated in acontinuous heat eX- changer by means of combustion gases.

JAMES M. RUMPLE.

